JP2978865B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer or a facsimile using an electrophotographic process, and more particularly to an image forming apparatus capable of stably supplying toner to an electrostatic latent image carrier for a long period of time.

[0002]

2. Description of the Related Art A conventional image forming apparatus includes a photosensitive drum (electrostatic latent image carrier), a developing device, and a power supply. The developing device includes a developing roller that supplies toner to the photosensitive drum, a supply roller that supplies toner to the developing roller, and a thin layer of toner that is supplied to the developing roller to regulate the amount of toner attached and the amount of charge to the developing roller. And a thin layer forming member. A bias voltage and a current are applied from a power source to the supply roller and the thin layer forming member, and a constant voltage is applied to the rotation shaft of the developing roller.

When the electrostatic latent image on the photosensitive drum is developed with toner, the toner supplied to the developing roller by the rotation of the supply roller and the developing roller in sliding contact is made uniform by the thin layer forming member on the developing roller. And thinned. At this time, the toner is charged at the time of friction between the supply roller and the developing roller and at the time of friction between the thin layer forming member and the developing roller, and is supplied from the developing roller to the photosensitive drum.

FIG. 8 is a graph showing an applied bias characteristic in a conventional image forming apparatus. The shaded part of the graph is
An area A having good printing (printing) is shown. The graph shown by the dashed line is the first conventional example when the constant voltage control is performed at -600 [V]. In this conventional example, by supplying a constant voltage of −600 [V] to the supply roller and the thin layer forming member, the variation of the toner charge amount on the developing roller is reduced, and the developing roller is reduced with printing. Of the toner is suppressed. Generally, the value of the constant voltage is the same value as the constant voltage Vb applied to the developing roller, or a value larger than this value Vb.

On the other hand, a graph shown by a dashed line is a second conventional example, in which an image forming apparatus described in Japanese Patent Application Laid-Open No. 9-106172 discloses a type in which a constant current is applied to a supply roller and a thin layer forming member. Show characteristics. In the second conventional example, the same effect as in the first conventional example is obtained by supplying a constant current of 3 [μA] to the supply roller and the thin layer forming member.

In the first and second conventional examples, the developing device impedance characteristic in the near-life state, which is the use limit, is higher than in the new state immediately after the start of use.
A current value or a voltage value applied to the supply roller and the thin layer forming member is lower in a state near the end of life than in a new product.

FIG. 9 is a graph showing a correlation between a potential difference and fog. As for the fog (ID) in the figure, the smaller the value, the less the toner-covered portion (dirt) and the better the image. When the potential difference | Vsr−Vb | between the voltage Vsr applied to the supply roller and the thin layer forming member and the voltage Vb applied to the developing roller is reduced, the toner charge amount is reduced and printing defects such as white background fog often occur. Can be seen from the graph. FIG. 10 is a graph showing a correlation between a current value and fog. From this graph, when the current Isr applied to the supply roller and the thin layer forming member is reduced,
As in the case of the above potential difference, it can be seen that the toner charge amount is reduced and printing defects such as white background fog often occur.

As described above, when the voltage Vsr or the current Isr increases, the applied voltage Vb to the developing roller is affected, and the applied voltage Vb, the voltage Vsr, or the current Isr does not show a constant value, and the waveform is always disturbed. State. This makes it difficult to charge the toner on the developing roller to make the toner uniform.

FIG. 11 shows the product of voltage Vsr and current Isr and I
9 is a graph showing a correlation with an sr amplitude value. In the figure,
The disturbance of the waveform is represented by the amplitude value Δ of the Isr current waveform, and the product of the voltage Vsr and the current Isr is defined as an absolute value Wsr [mW].
From the graph, it can be understood that the amplitude value Δ tends to increase as the absolute value Wsr increases.

[0010]

For example, a developing device is shown in FIG.
In order to obtain a good printing state by applying the applied voltage Vb of -400 [V] when the developing device impedance characteristic is provided in the first conventional example, a supply roller of 3.0 [mu] A or more supplies current Isr. And it is necessary to provide it to the thin layer forming member.

Here, as an example, a case where the absolute value Wsr of the product of the voltage Vsr and the current Isr applied to the supply roller and the thin layer forming member needs to be 2.5 [mW] or less will be described. For example, in the first conventional example in FIG.
The bias applied to the supply roller and the thin layer forming member is-
Since constant voltage control is performed at 600 [V], a current Isr of about 4.0 [μA] is required at the beginning of use (new), and about 2.3 [μA] at the end of use (near life). ] Is required. In this case, although the absolute value Wsr [mW] does not exceed 2.5 [mW] at both the initial and final stages of use, the current Isr is lower than 3.0 [μA] at the final stage. That is, the current I supplied to the supply roller and the thin layer forming member
Since sr decreases as the number of prints increases, it is extremely difficult to suppress a decrease in the toner charge amount on the developing roller. As a result, the dot sharpness is degraded, and the resolution of halftone dot shading is reduced, or problems such as deterioration of print quality due to thickening of characters are likely to occur. Further, a problem such as a toner fogging phenomenon in which the toner adheres to a portion that should become a white background without attaching the toner is likely to occur.

On the other hand, when the developing device has the developing device impedance characteristic in the second conventional example of FIG.
A] to obtain a good printing state by supplying the current Isr of
It is necessary to apply a voltage Vsr of about -550 [V] at the beginning of use and a voltage Vsr of about -650 [V] at the end of use in common to the supply roller and the thin layer forming member. In this case, the voltage Vsr applied to the supply roller and the thin layer forming member increases as the number of times of printing increases, and the same problem as described above easily occurs.

In view of the above, the present invention effectively suppresses the phenomenon that the charge amount of the toner on the developing roller decreases as the number of prints (prints) increases, and stably supplies the toner to the electrostatic latent image carrier. It is another object of the present invention to provide an image forming apparatus capable of maintaining a good printing state for a long period of time.

[0014]

In order to achieve the above object, an image forming apparatus according to the present invention comprises an electrostatic latent image carrier and a toner image formed on the electrostatic latent image carrier. And a supply roller that supplies toner while contacting the developing roller; a thin layer forming member that regulates the amount of toner and the amount of toner charged on the developing roller while contacting the developing roller; In an image forming apparatus including a supply roller and a power supply unit for applying a voltage Vsr and a current Isr to the thin layer forming member, the relationship between the voltage Vsr and the current Isr is represented by the following equation: | Vsr | / a + | Isr | / B = 1 (where a and b are constants of power supply characteristics).

In the image forming apparatus of the present invention, the voltage Vsr and the current Isr applied to the supply roller and the thin layer forming member at the time of image formation vary between the initial stage and the final stage of use.
While maintaining the relationship of Vsr | / a + | Isr | / b = 1, it changes so as to pass through the good printing region in the applied bias characteristic. As a result, from the beginning to the end of use, a decrease in the toner charge amount on the developing roller can be effectively suppressed, and the supply of toner to the electrostatic latent image carrier can be stabilized.

Here, when a constant voltage Vb is applied to the developing roller, it is preferable that the constant a of the power supply characteristic satisfies the condition of a> | Vb | and the constant b satisfies the condition of b> 3. In this case, the values of the constants a and b are optimally set, and
It is possible to further enhance the effect of suppressing the decrease in the toner charge amount.

More preferably, the power supply means includes an adjustment means capable of adjusting at least one of constants a and b of the power supply characteristic. In this case, the state in which the toner charge amount is suppressed from being reduced can be appropriately adjusted, so that the halftone density, the solid black density, and the like can be adjusted.

Preferably, the power supply means includes a constant voltage power supply, and a variable resistor inserted between the supply roller and the thin layer forming member and the constant voltage power supply, and the adjustment means includes the variable resistance power supply. Consisting of vessels. In this case, the adjusting means can be configured very simply.

[0019]

The present invention will be described in more detail with reference to the drawings. FIG. 1 is a sectional view showing the image forming apparatus according to the first embodiment of the present invention as viewed from the front. The image forming apparatus includes a photosensitive drum (electrostatic latent image carrier) 101 rotating in one direction, a charger 121 for charging the surface of the photosensitive drum 101, an exposure device (not shown), and a toner remaining on the photosensitive drum 101. The image forming apparatus includes a toner collecting unit 122 that scrapes and stores the toner, a developing unit 106, and a power supply unit 301.

The developing device 106 includes a developing roller 102, a storage case 105 for storing a nonmagnetic one-component toner T,
A supply roller 103 for supplying the toner T in the storage case 105 to the developing roller 102 and a thin layer forming member 104 are provided. The developing roller 102 contacts the photosensitive drum 101 and supplies the toner T to the electrostatic latent image formed on the photosensitive drum 101. The thin layer forming member 104 is provided with the developing roller 10.
The toner T supplied to the developing roller 2 is made uniform and thin, and the amount of toner attached and the amount of charge on the developing roller 102 are regulated.

The power supply section 301 includes a constant voltage power supply 301a and a fixed resistor 301b, and is connected to the supply roller 103 and the thin layer forming member 104 via the output terminal Z. And a bias voltage and current. A stirring member 105a that supplies the supply roller 103 to the supply roller 103 while stirring the toner T by rotating in one direction is provided in the storage case 105.

The developing roller 102 includes a thin layer forming member 104.
In consideration of the contact pressure between
An elastic material of about 25 to 60 degrees in IS-A is used. This elastic material is selected in consideration of leakage caused by low resistance between the thin layer forming member 104, the photosensitive drum 101, and the supply roller 103, or deterioration of development efficiency caused by high resistance. In order to realize this, for the development of the elastic material, a recon or a urethane which can make the resistance value between the surface of the roller 102 and the rotating shaft 102a about 10 ⁴ to 10 ⁸ [Ω] is used. About -250 to-
A constant voltage bias Vb of about 500 [V] is applied.

The supply roller 103 has a cell number of about 80 to 150 cells per inch, and about 10 ³ to 10 ¹⁰
It is made of a porous elastic material such as silicon or urethane including a conductive sponge or an insulating sponge having an electric resistance of about [Ω].

The thin layer forming member 104 is made of a spring member made of a thin metal plate such as stainless steel or phosphor bronze, or a material obtained by bonding an elastic material such as silicon or urethane having conductivity to the thin metal plate. Pressed with uniform contact pressure. This contact pressure is desirably about 1 to 15 [gf / mm]. The number of the thin layer forming members 104 is not limited to one, but may be plural.

In the image forming apparatus according to the present embodiment, a bias voltage V is applied from a power supply 301 to an output terminal Z for applying a bias to the supply roller 103 and the thin layer forming member 104.
sr and current Isr are supplied, and a power supply characteristic that satisfies the following equation (1): | Vsr | / a + | Isr | / b = 1 (where a and b are constants of the power supply characteristic) (1) I have.

Next, the operation of the image forming apparatus according to this embodiment will be described. When an electrostatic latent image is formed by the exposure device on the surface of the photosensitive drum 121 charged by the charge from the charger 121, the developing roller 102 supplies the toner T to the photosensitive drum 101. At this time,
The toner T supplied to the developing roller 102 is made uniform and thin by the thin layer forming member, and the developing roller 1
02 at the time of friction between the supply roller 103 and the developing roller 1
02 and the thin layer forming member 104 are charged at the time of friction. When the thin layer toner T charged on the developing roller 102 contacts the photosensitive drum 101, the photosensitive drum 101
The upper electrostatic latent image is developed.

A bias is applied to the supply roller 103 and the thin layer forming member 104 in order to suppress the reduction and the variation of the toner charge amount on the developing roller 102 described above.
As already described in the prior art, the area A with good print quality shown in FIG. 2 can be obtained by considering the respective characteristics shown in FIGS. Outside the area A, the toner is not sufficiently charged on the developing roller 102, and problems such as deterioration of dot sharpness, density unevenness, toner fogging on a white background, and thickening of characters are likely to occur.

FIG. 2 is a graph showing the applied bias characteristics of the voltage and current applied to the supply roller 103 and the thin layer forming member 104. A hatched area A in the figure indicates a range equivalent to the area A in FIG. 8, and the absolute value Wsr of the product of the voltage Vsr and the current Isr is set to 2.5 [mW] or less.

The bias voltage Vsr [V] and the current Isr [μ
A] changes during the period from the initial (new) use of the developing device 106 to the end (near life). In the present embodiment, the constants a and b of the power supply characteristics are set so that the bias voltage Vsr and the current Isr intersect with the developing device impedance characteristic curves at the initial and final stages of use in the region A. This makes it possible to maintain an optimal relationship between the bias characteristics applied to the supply roller 103 and the thin layer forming member 104 satisfying the condition of the above formula (1) and the developing device impedance characteristics. In FIG. 2, constants a and b of the power supply characteristics are set to a = 800 and b = 16, respectively, and the constant voltage bias Vb applied to the developing roller 102 is −400.
[V] is set.

By maintaining the bias characteristic and the developing device impedance characteristic satisfying the above expression (1) in an optimal relationship, the charged state of the toner T on the developing roller 102 is maintained uniform, and the developing roller 102 It is possible to suppress the above-described decrease in the toner charge amount. In addition, it can solve problems such as deterioration of dot sharpness, density unevenness, toner fogging phenomenon on white background, thickening of characters, etc., and maintain good print quality for a long time from the beginning to the end of use. can do.

In order to obtain a bias characteristic satisfying the above equation (1), a constant voltage power supply 301a that outputs a constant voltage a [V]
And a fixed resistor 301 b having a resistance value R of a / b [MΩ] are provided in the power supply unit 301. In this case, the constant voltage power supply 3
If the voltage value a [V] of the fixed resistor 301b and the resistance value a / b [MΩ] of the fixed resistor 301b can be changed, | Vsr | /
constants a and b in the power supply characteristic of a + | Isr | / b = 1
Can be set to a desired value.

FIG. 3 is a front sectional view of an image forming apparatus according to a second embodiment of the present invention. In the present embodiment, the configuration of the power supply unit 301 in the first embodiment is different,
Other configurations are the same. That is, the fixed resistor 301b provided inside the power supply unit 301 in the first embodiment.
However, in the present embodiment, the developing unit 10 outside the power supply unit 301 is
6. According to the present image forming apparatus having this configuration, the same effects as in the first embodiment can be obtained.

[0033]

Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. In the image forming apparatus according to the present embodiment, the process speed is set to 90 [mm / sec]. The developing roller 102 has an electric resistance value of 10 ⁵ to 10.
⁷ [Ω], a surface roughness Rz5 to 19 [μm], and a rubber hardness of 45 ° to 55 ° according to JIS-A.
[V] is applied. The supply roller 103 is made of a conductive urethane foam material. The thin layer forming member 104 is made of a stainless spring material having a thickness of 0.1 [mm] with a bent end portion, and comes into contact with the developing roller 102 with a contact pressure of 5 to 15 [gf / mm]. The toner T is made of a polyester resin material and has a volume resistivity of about 10 ¹⁰ to 10 ¹⁵ [Ω · cm].

From the graph of FIG. 9, the ground fog ID of the white background portion
To suppress the concentration to 0.01 or less, the potential difference | Vsr−Vb
| Is 0 [V] or more at the beginning of use and about 200 at the end of use.
It is understood that it is necessary to set the value to [V] or more. Therefore, | Vsr | is set to about 400 [V] or more at the beginning of use, and | Vsr | is set to about 600 [V] or more at the end of use. Further, from the graph of FIG. 10, in order to suppress the background fog ID concentration in the white background portion to about 0.01 or less, | Isr | is set to 0 [μA] or more at the early stage of use and about 3.0 [μA] or more at the end of use. It is necessary to set to. Further, from the graph of FIG. 11, it is recognized that as the absolute value Wsr of the product of the voltage Vsr and the current Isr increases, the amplitude value Δ of the current waveform of the current Isr tends to increase. It can be seen that it is necessary to set the absolute value Wsr to about 2.5 [mW] or less in order to suppress the value to [A] or less.

The area A in FIG. 2 satisfies all the above-described conditions described with reference to FIGS. When the power supply characteristic (bias characteristic) of the power supply unit 301 in FIG. 1 satisfies | Vsr | / 800 + | Isr | / 16 = 1, the above-described problem is solved, and a long-term operation is performed from the beginning to the end of use. And good print quality can be maintained. At this time, the bias voltage Vsr of -600 [V] and 4 [μ]
A] is supplied from the output terminal Z, and a bias voltage Vsr of −650 [V] and a bias current Isr of 3.0 [μA] are supplied from the output terminal Z to the developing device 106 at the end of use. I do.

Bias characteristic | Vsr | in the first embodiment
/ 800 + | Isr | / 16 = 1 means that the constant voltage application value a of the constant voltage power supply 301a shown in FIGS.
It can be obtained by setting to [V] and using a fixed resistor 301b having a resistance value R of 50 [MΩ].

Embodiment 2 In the image forming apparatus according to the present embodiment, the process speed is set to 52 [mm / sec]. The developing roller 102 has an electric resistance value of 10 ⁵ to 10 ⁷ [Ω] and a surface roughness of Rz ⁵ to 1
It is made of urethane rubber of 0 [μm] and rubber hardness of 45 to 55 ° in JIS-A, and -380 [V] is applied as a constant voltage bias Vb. Supply roller 103
Is made of a conductive urethane foam material. Thin layer forming member 1
04 has a thickness of 0.1 with a bent end portion.
[Mm] stainless steel spring material, 5-15 [gf / m
m] with the developing roller 102. Toner T
Is made of a material of a polyester resin, ¹⁰ 10-10
^It has a volume resistivity of about ¹⁵ [Ω · cm].

Under the above settings, the characteristics are set in the same manner as in the first embodiment. At this time, the power supply characteristic of the power supply unit 301 is set to | Vsr | / 560 + | Isr | /15.5=1. The power supply characteristic is such that the constant voltage applied value a of the constant voltage power supply 301a in FIGS. 1 and 3 is -560 [V].
And a fixed resistance 301b having a resistance value R of 36 [MΩ] can be obtained.

As can be understood from the first and second embodiments, when the power supply characteristic | Vsr | / a + | Isr | / b = 1 (where a and b are constants of the power supply characteristic) according to the present invention, the constant a is a> | Vb |. Further, the constant b is set to b> 3 (that is, 3 [μ
A]), the developing roller 1
02 can be reduced, the decrease in the toner charge amount on the developing roller 102 due to the increase in the number of prints can be suppressed, and good print quality can be obtained over a long period of time from the beginning to the end of use. Can be maintained.

Process speed, developing roller 102, constant voltage bias Vb, supply roller 103, thin layer forming member 1
Although the area A in FIG. 2 changes depending on conditions relating to the number of prints 04 and the toner T, or the number of prints and the temperature and humidity, optimal conditions can be set by changing the constants a and b of the bias characteristics.

FIG. 4 is a front sectional view of an image forming apparatus according to a third embodiment of the present invention. Also in the present embodiment, the configuration of the power supply unit 301 is different from that of the first embodiment.
Other configurations are the same. That is, in the present embodiment,
The fixed resistor 301b according to the first embodiment is disposed inside the power supply unit 301 as a variable resistor 301c. According to the present image forming apparatus having this configuration, the same effects as in the first embodiment can be obtained.

In the image forming apparatus of this embodiment, by adjusting the resistance value R of the variable resistor 301c, | Vsr | / a + | Isr | / b = 1 (where a and b are constants of the power supply characteristic) ) Can be freely changed. In this case, b is a value obtained by dividing the output voltage value a [V] of the constant voltage power supply 301a by the set value of the variable resistor value R (b = a /
R).

For example, a description will be given with reference to the case of the first embodiment. In the third embodiment, the output voltage value of the constant voltage power supply 301a is -800 V, and the variable resistor 301
The variable region of c is set to 30 to 75 [MΩ]. Here, the voltage Vsr and the current Isr applied to the supply roller 103 and the thin layer forming member 104 have the following characteristics shown in FIG. FIG. 5 is a graph showing the applied bias characteristics in the third embodiment. In this graph, when the resistance value of the variable resistor 301c is set to 30 [MΩ], when it is set to 50 [MΩ], it is 75 [MΩ].
Ω]. That is: | Vsr | / 800 + | Isr | /26.7=1: | Vsr | / 800 + | Isr | / 16 = 1: | Vsr | / 800 + | Isr | /10.7=1

As described above, when the developing device 106 is in the initial stage of use, the resistance value R of the variable resistor 301c is set to 50 to 75 [M
Ω], and in the last stage, the resistance value R is set to 30 to 50.
It can be seen that the above problem can be solved by setting [MΩ]. In particular, in the first embodiment, the developing device 10
In the case where 6 is the last stage, after setting the resistance value R to 50 [MΩ], the voltage Vsr was set to -650 [V], and the current Isr was set to 3.0 [μA]. On the other hand, in the present embodiment, after setting the resistance value R to 30 [MΩ], the voltage Vsr is set to −700 [V], and the current Isr is 3.7 [μA].
, Both the voltage Vsr and the current Isr are increased from the case where the resistance value R is 50 [MΩ].

Here, referring to FIGS. 9 and 10, it can be seen that as the voltage Vsr and the current Isr increase, the margin for the background fog of the white background increases. Therefore, when the resistance value R is set to 30 [MΩ], the margin for the ground fog is wider than when the resistance value R is set to 50 [MΩ], and is larger as a solution to the above-described problem. The effect can be obtained.

FIG. 6 is a graph showing the correlation between the total number of rotations of the photosensitive drum and the resistance of the variable resistor when the resistance is automatically adjusted. As the variable means of the variable resistor 301c, there are a manual method in which a user manually adjusts and an automatic method in FIG.

When the manual method is adopted, the resistance value R of the variable resistor 301c can be adjusted manually.
, It is possible to change the solid black density, the halftone dot density, or the halftone dot resolution to adjust the density and the gradation to the user's preference. On the other hand, when the automatic method is adopted, the control unit (not shown) recognizes the rotation speed of the photosensitive drum 101 or the developing roller 102, and automatically adjusts the resistance value R as the rotation speed increases. I do. In the automatic method, for example, when the developing device 106 is in the initial stage of use, the resistance value R is set to about 75
[MΩ], and is automatically adjusted so that the resistance value R becomes about 30 [MΩ] at the end of printing of 11,000 pages. Thereby, a greater effect can be obtained.

FIG. 7 is a front sectional view of an image forming apparatus according to a fourth embodiment of the present invention. Also in the present embodiment, the configuration of the power supply unit 301 is different from that of the first embodiment.
Other configurations are the same. That is, the variable resistor 301c provided inside the power supply unit 301 in the first embodiment.
However, in the present embodiment, the developing unit 106 is provided outside the power supply unit 301. With the image forming apparatus having this configuration, the above-described problem can be solved and the same effects as those of the first embodiment can be obtained.

As described above, the present invention has been described based on the preferred embodiment. However, the image forming apparatus of the present invention is not limited to the configuration of the above-described embodiment, and the configuration of the above-described embodiment is not limited thereto. An image forming apparatus in which various modifications and changes are made is also included in the scope of the present invention.

[0050]

As described above, according to the image forming apparatus of the present invention, the phenomenon that the toner charge amount on the developing roller decreases as the number of prints increases is effectively suppressed, and the electrostatic latent image carrier And it is possible to maintain a good printing state for a long period of time.

[Brief description of the drawings]

FIG. 1 is a front sectional view of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a graph showing bias characteristics in the first embodiment.

FIG. 3 is a front sectional view of an image forming apparatus according to a second embodiment of the present invention.

FIG. 4 is a front sectional view of an image forming apparatus according to a third embodiment of the present invention.

FIG. 5 is a graph showing an applied bias characteristic in the third embodiment.

FIG. 6 is a graph showing a correlation between the total number of rotations of the photosensitive drum and the resistance value of the variable resistor.

FIG. 7 is a front sectional view of an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 8 is a graph showing a conventional applied bias characteristic.

FIG. 9 is a graph showing a correlation between a potential difference and fog.

FIG. 10 is a graph showing a correlation between a current value and fog.

FIG. 11 is a graph showing a correlation between an absolute value of a product of a voltage value and a current value and an amplitude value of a current waveform.

[Explanation of symbols]

 Reference Signs List 101 photoconductor drum 102 developing roller 103 supply roller 104 thin layer forming member 106 developing device 301 power supply unit 301a constant voltage power supply 301b fixed resistor 301c variable resistor Z output terminal

Claims (4)

(57) [Claims] An electrostatic latent image carrier, a developing roller for supplying toner to an electrostatic latent image formed on the electrostatic latent image carrier, and a supplying roller for supplying toner while being in contact with the developing roller Roller, a thin layer forming member that regulates the toner amount and the toner charge amount on the developing roller while being in contact with the developing roller;
In an image forming apparatus comprising: a power supply unit that applies a voltage Vsr and a current Isr to the supply roller and the thin layer forming member, the relationship between the voltage Vsr and the current Isr is represented by the following equation: | Vsr | / a + | Isr | / B = 1 (where a and b are constants of power supply characteristics). 2. When a constant voltage Vb is applied to the developing roller, the constant a of the power supply characteristic satisfies the condition of a> | Vb | and the constant b satisfies the condition of b> 3. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 1, wherein the power supply unit includes an adjustment unit that can adjust at least one of constants a and b of the power supply characteristic. 4. The power supply means includes a constant voltage power supply, and a variable resistor inserted between the supply roller and the thin layer forming member and the constant voltage power supply, and the adjusting means includes a variable resistor. 4. The image forming apparatus according to claim 3, comprising a container.